In various surgical procedures it is desired to anchor a structure in bone; for example, in replacement of damaged anterior cruciate ligaments (ACLs) it is usual to bore tunnels through the opposed bones of the knee joint and anchor a replacement ligament thereto using interference screws. Numerous patents and publications address various aspects of such procedures and provide suggestions to solve various problems connected therewith; see U.S. Pat. Nos. 5,645,547 to Coleman and 5,871,504 to Eaton et al. The Eaton patent in particular illustrates the need for a firm and reliable anchoring technique whereby the ends of a replacement ligament are fixed to the inner walls of tunnels in the bones using threaded fasteners.
As is well known, bones, in particular the long bones such as those of the leg, have a composite structure wherein a hard, dense outer cortex encapsulates a mass of cancellous bone. The tunnels within which replacement ligaments are anchored extend through this cancellous bone, which is relatively soft and spongy, and does not provide good holding for threaded fasteners and the like. In order to improve the holding power of the cancellous bone, it is known to compact the bone surrounding the tunnels, forming a denser structure better adapted to hold threaded fasteners. Typically this has been done by successively driving a series of “torpedo”-shaped members through the tunnels using a hammer; this technique can be used to increase the diameter of a tunnel from 6 mm to 10–12 mm using a series of torpedoes of diameters increasing in 0.5 mm increments. However, this technique is rather crude, involves excessive numbers of steps and of tools, and is generally unsatisfactory.
The art shows several varieties of tools for dilating soft tissues, e.g., for creating space within which to carry out a surgical procedure. See U.S. Pat. Nos. 6,436,119 to Erb et al, and 5,888,196, 5,685,826 and 5,454,365 to Bonutti. Molesworth U.S. Pat. No. 319,296 shows a device described as a combined dilator, drainer, injection and suction syringe. The Molesworth device comprises an outer tubular member which is slit longitudinally from one end so as to form a series of spring prongs defining a segmented outer surface. A tapered inner member can be urged along the lumen of the tubular outer member to force the prongs outwardly, expanding the segments of the outer surface in order to dilate a wound, for example, to enable better irrigation thereof. There is no suggestion in Molesworth that such a device would be of use in compacting cancellous bone in order to better secure an interference screw or the like, and it would seem that friction within the Molesworth device would be excessive in use for such a purpose. Moreover, the Molesworth prongs are not constrained to move outwardly parallel to one another, and so would not be useful in forming a tunnel of regular cylindrical shape in the compacted cancellous bone, as is desired for convenient fixation of anchoring structures.
Accordingly, the art requires a better tool adapted and optimized specifically for dilating and compacting the walls of tunnels formed in cancellous bone to form a tunnel of cylindrical shape.